Observations of accretion shocks

Ardila, D. R.

doi:10.1017/s1743921307009465

Cited by 1 publication

(2 citation statements)

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“…In this poster, we focus primarily in explaining the UV lines observations from [7]. A more complete study of the outstanding problems can be found in [1].…”

Section: Contextmentioning

confidence: 99%

“…Resolved observations of C IV and other "transition region" lines for a handful of CTTSs, reveal that the lines are broad (∼300 km/s) and present a diversity of centroids, from very blueshifted (like DG Tau) to moderately redshifted (like DR Tau) [1]. If the line emission from stars with moderate accretion rates is dominated by pre-shock emission (with flow velocities of a few hundred km/s towards the star), why are the lines not redshifted?…”

Section: Open Questionsmentioning

confidence: 99%

See 1 more Smart Citation

A Consistent Model of the Accretion Shock Region in Classical T Tauri Stars

Ardila

Johns-Krull

2009

AIP Conference Proceedings

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Abstract.We develop a consistent model of the accretion shock region in Classical T Tauri Stars (CTTSs). The initial conditions of the post-shock flow are determined by the irradiated shock precursor and the ionization state is calculated without assuming ionization equilibrium. Comparison with observations of the C IV resonance lines (λ λ 1550 Å) for CTTSs indicate that the post-shock emission predicted by the model is too large, for a reasonable range of parameters. If the model is to reproduce the observations, C IV emission from CTTSs has to be dominated by pre-shock emission, for stars with moderate to large accretion rates. For stars with low accretion rates, the observations suggest a comparable contribution between the pre-and post-shock regions. These conclusions are consistent with previous results indicating that the post-shock will be buried under the stellar photosphere for moderate to large accretion rates. CONTEXTClassical T Tauri Stars (CTTSs) are young, low mass stars, accreting from a circumstellar disk. Their spectra show strong excess emission over a broad range of wavelengths. These excesses result from the presence of the accretion disk and its interaction with the stellar magnetic field. In particular, the excess line emission at optical wavelengths has been successfully modeled (e.g. [10]) as being due to the presence of gas captured in the extended magnetosphere. The continuum excess is believed to be primarily due to heating of the stellar photosphere by the same gas as it falls into the star [2].Line excesses are also observed at UV wavelengths, and the observational problem is conceptually similar to the optical one, although the shorter wavelengths imply that the lines trace higher energy processes. As in the optical, surface fluxes are much larger than expected from a naked atmosphere. [7] have showed that the surface flux in the C IV resonant lines (λ λ 1550 Å) can be as much as an order of magnitude larger than the largest flux observed in Weak T Tauri stars (WTTs), main sequence dwarfs, or RS CVn stars. They have also showed that the excess flux in the lines is strongly correlated with accretion rate, suggesting that the lines are powered by the accretion process.The diagnostic power of these observations is limited due to the lack of complete, self-consistent models of the region. We have developed such a model, with the goal of

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“…In this poster, we focus primarily in explaining the UV lines observations from [7]. A more complete study of the outstanding problems can be found in [1].…”

Section: Contextmentioning

confidence: 99%

Section: Open Questionsmentioning

confidence: 99%